Electromagnetic unit



A..M. COHEN 2,875,383 I ELECTROMAGNETIC UNIT Feb. 24, 1959 Original Filed Jan. 8, 1953 4 Sheets-Sheet l T i c INVENTOR.

WM/W

Feb. 24, 1959 A. M. COHEN ELECTROMAGNETIC UNIT 4 Sheets-Sheet 2 Original Fi led Jan. 8, 1953 IE. 2 l A INVENTOR. Air/7'02 M. COHEN A TTOP/VEYS' Feb. 24, 1959 A. M. COHEN ELECTROMAGNETIC UNIT 4 She'ecs-Sheet 3 Original Filed Jan. 8, 1953 N & 5 3 MC W. M w H m A ATTOEA/EXS Feb. 24, 1959 A. M. COHEN ELECTROMAGNETIC UNIT 4 Sheets-Shet 4 Original Filed Jan. 8 1953 INVENTOR. 427 /02 M. caye/v 2,875,383 Patented rats. 24, 1959 ice 2,875,383 ELECTROMAGNETIC UNIT Arthur M. Cohen, Westport, Conn.

Continuation of application Serial No. 330,259, January 25,; This application August 27, 1957, Serial No.

22 Claims. (Cl. 317-198) The present invention relates to the construction of an electromagnetic unit, and in particular to the mounting and arrangement or" the electromagnetic driving elements and the parts moved thereby, to the end that the operation of the unit should be independent of position, shock or vibration, with an extremely high degree of of sensitivity and speed of response.

Electromagnetic units of the type under discussion are suitable for many uses, but are particularly adapted for use as theenergizing and driving component of a fingertype circuit controlling device such as that disclosed in my Patent No. 2,580,732 of January 1, 1952, entitled Finger-Type Circuit Regulator. In that patent there is disclosed a device of extremely small size and low weight provided with ten contact pairs adapted to be sequentially opened and closed in accordance with the increase or decrease in energization of an electromagnet. ecause of the dynamic characteristics of the moving parts of the unit there disclosed, it is far more than a mere sequential relay or voltage regulator. It is, indeed, a true servomechanism which, when connected in a circuit including feedback, provides for servo control with a substantially zero steady state error and which, because of the highspeed averaging effect which occurs between adjacent contact pairs, provides effective stepless control at power frequencies. Those and comparable operational characteristics have resulted in a great demand for such units in applications of widely ranging characters.

One limitation on the useability of such units derives from the fact that they have but ten contact pairs, and the life of the unit is limited by the current carried by those contact pairs at the moment of break and the voltage across those pairs at the moment of break. The use of ten contact pairs, in some installations, will not provide for proper control over a sufficiently wide range without adversely affecting the life of the unit.

The obvious answer is to provide the unit with a greater number of contact pairs, and this was tried early in the history of the development of the unit. However, providing additional contact pairs gave rise to other problems the solution of which, although sought over an extended period of time, was not easy to come by. A greater number of contact pairs meant that larger moving parts were required, and this in turn called for an increase in the attractive force of the electromagnet, difficult to attain within rigidly limited size, weight and power specifications. The mechanical problems, both static and dynamic, particularly the latter, were most troublesome, particularly when it is borne in mind that the moving parts of the unit must have a sufficiently rapid speed of response to provide for stepless control, that the moving parts must be capable of being adjustably damped over a wide range so that the unit may be used in a wide variety of servo applications without hunting, and that, because of the large number of contact pairs which must be opened or closed in an accurately predetermined sequence, the permissible range of movement of the moving parts is'necessarily must greater than in the smaller unit. In addition, the unit must operate equally well in any position, and even when subjected to great shock or vibration or high accelerative force s, since units of this type are often used in combat aircraft and missiles of various types. Moreover, it must be so dependable in operation as to require no maintenance over its expected life.

The electromagnetic unit here disclosed and claimed has thirty finger pairs, three times the number provided in the unit disclosed in the aforementioned Patent No.

2,580,732. Nevertheless, a careful redesign of the unit,

with particular reference to magnetic circuits and physical mounting of the moving parts so as to permit the armature to pivot with respect to the electromagnet in a substantially frictionless manner and so as to permit the contactlifting member to pivot with respect to the armature, has produced a unit which does not sacrifice any of the operating characteristics of the smaller unit and which controls the positioning of thirty contact pairs with only an inappreciable increase in power consumption over the small ten-contact-pair unit, all without excessively increasing the size of the unit. The unit of the present invention, including its cover, is less than 6 inches long, only slightly more than 2 inches wide, and less than 3 inches high, exclusive of the plug-in prongs.

It is necessary that the electromagnet should attract the armature with suflicient force so that it can operate properly over its entire range of movement. As the electromagnet moves it sequentially opens more and more contact pairs. The individual movable contacts of those pairs are resiliently urged toward their respective fixed contacts, and therefore the armature is acted upon by a greater and greater force in opposition to its direction of motion. If the unit is to operate in a substantially uniform manner over its entire range, the force exerted on the armature by the electromagnet must not only be suflicient to overcome the opposing force exerted by the reference or biasing springs directly active on the armature, but must also increase in a graduated manner conforming to the increase in that opposing force as more and more contact pairs are opened.

Thus the mounting of the armature with respect to the electromagnet is an extremely critical matter. The proper relationship of attractive forces to armature position is obtained by providing the armature with apertures through which the electromagnet cores are loosely received as the armature pivots toward the electromagnet, and the precise spatial relationship between the two is closely controlled. In the unit of Patent No. 2,580,- 732 this result was achieved by adjustably mounting the armature with respect to the electromagnet. Hence assembly of the parts involved precise relative positioning thereof, calling for a high degree of care and skill on the part of the individuals performing that task. According to the instant invention, however, the electromagnet is non-adjustably fixed to the same plate on which the armature is mounted, and that plate itself serves to accurately position both the electromagnet and the armature. This is accomplished by forming the plate of non-magnetic material and providing it with one or more apertures of closely the same size as the electromagnet core or cores, said cores passing through the apertures and thus being fixed in position relativeto the plate. The armature is connected to the plate by means of a flexible but non-extensible and non-contractible member such as a leaf spring, the spring thus normally preventing movement of the armature over the plate. Location of the points of attachment of the leaf spring to the armature and plate respectively are accurately determined in the fabrication of the respective parts in conventional manner, and assembly will necessarily result in proper relative positioning of the elements. Interengaging memare normally out of engagement but which are engageable when shock forces the armature to move over the plate, interengagement of said members positively limiting the degree of said movement so as to prevent permanent deformation of said leaf spring, the resiliency of said spring ensuring that the armature will return to its proper position. Thus the position of the armature relative to the plate, and hence to the electromagnet active thereupon, is fixed by the connections between the armature and the plate. Because the plate I on which the electromagnet is mounted serves to fix the position of the electromagnet relative thereto in the manner above described, the core or cores of the electromagnet snugly fitting in apertures in the plate, and because the armature is mounted on the opposite surface of the plate from the electro magnets, it is desirable that the plate be formed of some non-magnetic material. If this were not done the electromagnetic circuit from electromagnet to armature would be in effect short-circuited by the mounting plate, and hence insufficient attractive force would be exerted on the armature. In order to provide for a complete electromagnetic loop under these circumstances, the electromagnet is so constructed as to have a substantially U-shaped configuration defined by a pair of spaced cores and a bottom plate of magnetizable material, the cores being spaced in a balanced manner relative to the armature so that proper dynamic action is achieved. For purposes of electrical efficiency and in order to conserve space and reduce the size of the unit, two windings are provided, one on each core, the windings being so connected and Wound in such a direction as to produce an opposite polarity in each of the core tips, the armature itself, which is formed of magnetizable material, serving to link those tips and close the magnetic loop.

The armature must be mounted so as to be pivotal in a substantially frictionless manner in order to reduce losses. It must also be mounted in such a manner that, no matter what forces of acceleration, vibration or shock may be applied thereto, it will at all times retain its position relative to the electromagnet. To that end the armature is mounted so as to pivot about an edge of the plate on which the electromagnet is also mounted, the leaf spring previously adverted to providing for substantially frictionless pivoting. The leaf spring exerts a negligible effect in opposing or aiding the pivotal movement. The manner in which the armature is prevented from moving parallel to the plate when subjected to shock has already been explained. In addition, the armature is provided with elements engageable with ledges fixedly positioned with respect to and facing toward the plate, the interengagement between said elements and said ledges positively preventing the armature from moving away from the electromagnet even if the unit is subjected to extremely great accelerative or shock forces.

Because of the accumulated force of up to thirty resiliently urged movable contacts which may be active on the contact-lifting member at one time and the force of the reference or biasing springs, 21 new mode of connection of the contact-lifting member to the armature had to be devised, one which was strong enough to withstand the opposing force of the movable contacts but which would at the same time permit the contact lifting member to pivot with respect to the armature and thus retain an orientation of substantial perpendicularity with respect to the movable contacts, the desirability of such an orientation and pivotal mounting with respect to the armature having been brought out in Patent No. 2,580,732. In the unit of that patent the contact lifting member is connected to a resilient sheet which projects out from the armature itself, but in the large unit of the present invention this sheet did not have sufiicient strength to permit proper'action. Hence, the contact lifting member is secured to a metal sheet provided with slots within which arms extending rigidly from and preferably integral with the armature are received, the sheet being perpendicular to those arms and in line with the force exerted by the resilient contacts and the reference springs. Therefore, although that sheet is preferably thin and flexible, in order not to add unnecessary weight to the moving parts and in order to permit insertion of the armature arms within the slots, the forces exerted by the resilient contacts and reference springs will be active thereon in the direction of its height and not in the direction of its thickness. As a result the force of the movable contacts will be effectively contained, while the thinness of the sheet mounted on the armature arms together with the configuration of the interengaging surfaces, will permit the sheet to pivot with respect to those arms. rangement of this sheet further permits the attachment of the reference springs directly thereto, so that those springs may function not only to tend to restore the armature to its at-rest position but also to retain the contact-lifting member in proper orientation with respect to the movable contacts, all without distorting or weakening the sheet to which the contact-lifting member is secured or impairing its static and dynamic relationship to the armature and the other parts of the unit.

The unit of the present invention, like the unit of Patent No. 2,580,732, is designed for plug-in operation. This is an exceedingly important feature, since it permits the resistor network cut into and out of the circuit by the unit to be individually designed for the particular application for which the unit may be used without requiring any modification of the standard unit itself. It

has the further advantage that whatever heat-dissipative roblems may derive from the use of a particularresistor network will not affect the operation of the unit, since the resistors may be mounted remote from the unit. Because of the large number of prongs which must be provided to accommodate thirty contact pairs, some ditficulty in properly mounting the unit on a panel has been experienced. In order to eliminate this difficulty, the plugin prongs are divided into a plurality of groups each capable of fitting into standard sockets, and the unit is further provided with means independent of the prongs for securely mounting the unit on a panel, the panel being provided with one or more apertures through which the various groups of prongs project, the several sockets being engageable with the individual prong groups after the unit has first been firmly positioned on the panel.

To the accomplishment of the above, and to such other objects as may hereinafter appear, the present invention relates to the structure of an electromagnetic unit and the arrangement and interconnection of its parts as defined in the following claims and as described in this specification, taken together with the accompanying drawings, in which:

Fig. 1 is a rear elevational view of the unit of the present invention with the cover removed;

Fig. 2 is a front elevational view thereof;

Fig. 3 is a side elevational view thereof;

Fig. 4 is a cross sectional view taken along the line 4-4 of Fig. 2;

Fig. 4A is an enlarged view of a portion of Fig. 4;

Fig. 5 is a three-quarter perspective exploded view of the unit;

Fig. 6 is a three-quarter perspective view of the armature and leaf spring;

Fig. 7 is a fragmentary view, partially broken away, showing the manner in which the projecting portion of the armature core cooperates with apertures in the armature;

Fig. 8 is a top plan view of a panel to which the unit is adapted to be secured;

Fig. 9 is a cross sectional view taken along the line The ar- 99 of Fig. 8, and showing the unit in position on the panel; and

Fig. 10 is a schematic view indicating the electrical connection of the contact pairs and the electromagnet to the various plug-in prongs.

The unit comprises a base plate 2 of metal or the like on which a series of insulating plates 4, here shown as three in number, are secured by means of the screws 6, each of those plates carrying an appropriate number of plug-in prongs 8, the base plate 2 being apertured to permit those prongs to extend therebelow. Mounting screws 10 extend well below the tips of the prongs 8 (see Fig. 3), those screws 10 passing through the base plate 2 and appropriate ones of the insulating plates 4 and being secured in place by means of nuts 12. The base and insulating plates 2 and 4 may be considered as defining a mounting element.

Rear spacers 14 are secured to the base plate 2 by means of screws 15, the lower portion of the spacers 14 having enlarged heads 16 the upper surfaces of which define ledges 18. The mounting plate 20, defining the electromagnet bottom plate, is mounted on the spacers 14, upper sleeve spacers 22 are positioned thereabove, the magnet top plate 24 is mounted on the sleeve spacers 22, and screws 26 pass through the magnet top plate 24, the sleeves 22, and the mounting plate 20 and into the upper portion of the spacers 14, there being threadedly received. The plate 20 defines an end plate for the electromagnet. A comparable arrangement, comprising bottom spacers 28 under the mounting plate 20 and sleevelike upper spacers 30 between the mounting plate 20 and the magnet top plate 24, are provided forwardly of the just described rear spacer arrangement, screws 32 serving to secure the bottom spacers 28 to the base plate 2 and screws 34 passing through the magnet top plate 24, the sleeve-like spacers 30 and the mounting plate 20 and into the upper portion of the lower spacers 28, there being threadedly received. In this way the various spacers,

the mounting plate 20 and the magnetic top plate 24 define a rigid assembly fixed to the base plate 2. The spacers 14, 22, 28 and 30, as well as the mounting plate 20, are formed of some non-magnetic material such as brass. The magnetic top plate 24 may be formed of a magnetizable material such as Armco iron. The spacers 16 and 28 may be considered as defining supports for the electromagnet on the mounting element 2, 4.

The mounting plate 20 is provided at its sides with forwardly extending and downwardly bent arms 36 to which an angled bracket 38 is secured, that bracket in turn carrying insulating panel 40 on which the fixed contacts 42 and movable contact fingers 44 are appropriately mounted. The panel 40 is here illustrated as a single piece, but it could be made up of separate sections if desired. The movable contact fingers 44 are resilient and have tips which extend out beyond the fixed contacts 42. The contact pairs, each of which consists of a fixed contact 42 and a corresponding movable contact 44 resiliently urged into engagement therewith, are arranged side by side along the length of the unit. Appropriate electrical connections 46 are made between individual movable contacts 44 and appropriate plug-in prongs 8a, all of the fixed contacts 42 being electrically connected by means of bus bar 48, that bus bar 48 in turn being. connected to appropriate prong or prongs 8'12.

The configuration of the mounting plate 20 can best be seen from an examination of Fig. 5. Between the arms 36 at its sides, and rearwardly inse't relative thereto, is an edge 50, a portion 53 of the mounting plate 20 being centrally located and projecting forwardly therefrom. It is about the edge 50 that the armature, generally designated 52, is adapted to pivot.

The configuration of the armature 52 can best be seen from Fig. 6. It comprises a first portion 54 adapted to extend rearwardly from the edge 50 and over the mount- 6 ing plate 20 and a second portion 56 adapted to extend forwardly from the edge 50, said second portion '56 being provided with an opening 58 through which the projecting portion '53 of the mounting plate 20 is freely received. The side wings 60 of the armature 52 are provided with apertures 62 through which the front lower spacers 28 are adapted to freely pass. As may best be seen from Fig. 4, the upper portions 64 of those front lower spacers 28 have a diameter such that they will extend out to a slight degree beyond the inset edges 51 lo: cated outboard of the pivoting edges 50, thus defining ledges 66 substantially in line with and facing upwardly toward the lower surface of the mounting plate 20. The apertures 62 in the wing portion 60 of the armature 52 are considerably larger than the spacer portions 64 which extend therethrough, and those wing portions are pro-' vided with adjacent apertures 68 which receive screws 70 so that disks 72 may be mounted thereon, these disks 72 in turn having a diameter such that they extend over the" apertures 62 and over the ledges 66. The lower surfaces of the disks 72 therefore rest substantially on or are very closely spaced from the ledges 66, thus preventing the armature 52 from moving downwardly away from the mounting plate 20 to any appreciable degree.

The rear edges of the disks 72 are very closely positioned with respect to the edges 51 of the mounting plate 20, a slight clearance being provided sufficient to permit the armature 52 to pivot to the degree desired. As the armature 52 pivots in a clockwise direction as viewed in Fig. 4 the forward edge of the disk 72 will engage with the edge 51 of the mounting plate 20, thus acting as a positive stop if necessary. A further positive stop against pivotal movement of the armature 52 in that direction is provided by the ledge 18 defined by the enlarged lower portion 16 of the rear lower spacer 14, the end of the first armature portion 54 making engagement therewith.

The first portion 54 of the armature 52 is provided with a pair of carefully positioned apertures to receive screws 74 which also pass through carefully positioned apertures at one end of a leaf spring 76, the latter projecting forwardly into the armature opening 58. This spring may be formed of some suitable resilient material such as beryllium copper. The forwardly projecting end of the leaf spring 76 is provided with carefully positioned aper-' tures 78 through which pass screws 80 which secure the leaf spring 76 to accurately located holes in the forward- 1y projecting mounting plate portion 52. The positions of theapert'ures and holes for the screws 74' and 80 are precision controlled in manufacture by conventional means, and hence when the leaf spring 76 is secured to the armature 52 and mounting plate 20 respectively by the screws 74 and 80, the relative positions of those two members will be closely fixed. The fact that two screws 74 and 80 are used at each end of the leaf spring 76 pre vents rotative movement of the armature 52 on the plate 20.

The armature 52 is adapted to be attracted by an electromagnet 82 mounted between the magnet top plate 24 and the mounting plate 20 which serves structurally as the magnet bottom plate. The electromagnet 82 is provided with a pair of cores 86 which are internally threaded at their upper ends and are secured to the magnet top plate 24 by screws 88 which pass through accurately located apertures 90 in the top plate 24. In order to further fix the position of these cores 86 with precision, the bottom or mounting plate 29 is provided with a pair of apertures 92 each of closely the same shape and size as the projecting portions of the cores 86, those projecting coreportions snugly passing through the apertures 92 and'projecting' out beyond the lower surface of the mounting plate 20. The magnetic portion of the electromagnet 82 is thus substantially of U-shape, the parallel arms of which are defined by the cores 86 and the base of which is defined by the magnet top plate 24, all these elements being formed of magnetic material. As

has previously beenmentioned, the plate 20 is made of non-magnetizable material such as brass, and therefore does not enter the magnetic circuit, instead interposing a portion of low permeability between the core tips. In order to conserve space and at the same time provide an attractive force of sufiicient magnitude active on the armature'52,'and also in order to achieve a more efficient use of coil turns, a pair of windings 84, 84 are provided, one on each .of the cores 86. These windings 84, 84 are wound in such a direction and so connected that they are in series aiding around the magnetic loop, that is to say, so that opposite polarity is produced at any given instant at the tips of their respective cores 86.

Themagnetic loop is adapted to be completed by the first armature portion 54, which extends over those portions of the cores 86 which project beyond the lower surface of the mounting plate 20, being attracted thereby when the windings 84, 84 are energized. Since the armature portion 54 is formed of magnetizable material, a complete high-permeability magnetic loop is produced except for the small air gap between the armature portion 54 and the tips of the cores 86.

The first armature portion 54 is provided with apertures 94 which register with but are somewhat larger than the projecting portions of the cores 86. When the armature portion 54 is attracted by the electromagnet 82 and moves theretoward, pivoting in a counter-clockwise direction as viewed in Fig. 4, the projecting portions of the cores 86 freely enter the apertures 94. This varies the effective air gap in the magnetic loop and thus produces a rapid increase in electric pull exerted on the armature portion 54, the magnitude and rate of change of that electromagnetic pull being dependent upon the configuration of the projecting portions of the cores 64 and the spacing between them and the apertures 94. Hence it will be appreciated that accurate positioning of the, armature 52 relative to the electromagnet S2 is essential if proper operation of the unit is to be achieved.

The configuration of the projecting portions of the cores 86 and the spacing therebetween and the apertures 94 may be varied in manufacture over wide limits to produce any desired relationship between electromagnetic pull and armature position. The drawings show a particular stepped design for such a projecting core portion, the smaller tips 97 of the cores extending through slightly larger apertures 96 formed in a plate 98 of electromagnetic material mounted on that surface of the first armature portion 54 remote from the mounting plate 20 by means of screws 100. It will be understood, however, that other arrangements and configurations could be employed if desired.

Since the electromagnet windings 84, 84' are positioned directly on top of the upper surface of the mount ing plate 20, this being desirable in order to ensure efficient operation without detracting from accuracy of location of the various elements, the mounting plate 20 is provided with. slots 104 communicating with the apertures 92 in which the projecting portions of the cores 86 are snugly received and extending outwardly beyond the periphery of the windings 34, leads 106 from those windings 84 being receivable in and passing through the slots 104 and then extending to the upper surface of the mounting plate 20. Additional apertures 108 are provided, the leads 106 then being threadable down through the apertures 108 to an appropriate plug-in prong 80. When, as is here illustrated, the windings 84, 84' of the electromagnet 82 are connected in series aiding, so that both electromagnets will have an additive attractive effect on the armature 52, only one lead 106 from each winding 84 need pass through the slot 104 and aperture 108, the other leads 110 thereof being led off from the body of the windings 84, 84' at any appropriate point at their rear and being fixedly connected together at 112 (see Figs. 1 and 3).

The armature 52 is provided with arms 114 extending forwardly therefrom over the tips of the movable con tacts 44, the side surfaces of those arms being notched at 116. A contact-lifting member, in the form of a sheet 118 of insulating material or the like having an inclined lower edge 120, is secured to a thin plate 122 of some flexible material such as beryllium copper, the plate 122 having a pair of slots formed therein, each of the slots comprising a horizontal portion 124 and an angled access portion 126 extending to the upper edge of the plate 122, the slots being so spaced that the projecting armature arms 114 are receivable in the horizontal slot portions 124 with the notches 116 engaging the outer and inclined edges of the access slot portions 126. Notches 128 are preferably provided where the outer inclined edges of the access slot portions 126 meet the lower edges of the horizontal slot portions 124. By reason of this mounting the plate 122 and the contact-lifting member 118 will be carried and moved by the armature arms 114, will be pushed down and lifted by the armature 52 as it pivots, and at the same time the plate 122 and contact-lifting member 118 will be permitted a reasonable degree of pivotal movement about an axis perpendicular to the arms 114, and all in a substantially frictionless manner because of the edge contact between the plate 122 and the arms 114 and the flexibility of the plate 122.

Reference springs 130 are secured directly to the plate 122, by means of holes formed therein to either side of the access slot portions 126, the other ends of the springs being secured to arms 132 which extend forwardly from the magnet top plate 24. These reference springs 130 are in stretched condition, and consequently tend to pull the plate 122 upwardly, thus causing the armature 52 to tend to pivot in a clockwise direction as viewed in Fig. 4, the lower inclined edge 120 of the contact-opening member 118 then being removed from all of the movable contacts 44.

The magnet top plate 24 is provided with a central forwardly projecting portion 134 on which a dashpot 136 is mounted by means of screws 138, a slot 140 being provided for access to the dashpot adjusting screw 142. The dashpot piston is connected, by means of an L-shaped resilient connecting member 144, to the plate 122 via the hole 146 therein.

The unit, enclosed by a cover 148 shown only in Fig. 9, is adapted to be plugged into an external circuit which is specially designed for the installation which the unit is to control. Because of the large number of contact prongs 8 required by the use of so many contact pairs, difiiculty has been experienced in properly plugging the unit into a panel. In addition, non-standard sockets would be required, thus not only increasing the cost of the installation but, which is perhaps more significant from a military point of view, accentuating the problem of maintenance and spare parts. Therefore it is preferred to utilize a plurality of standard male plug-in units, as exemplified by the three separate insulating plates 4 carrying sets of plug-in prongs 8, in conjunction with a mounting panel 150 which may, if desired, be provided with three separate apertures 152 into each of which one of the standard sets of prongs 8 is adapted to project. Therefore standard female socket members 154 are provided for each standardset of prongs 8, each of the sockets 153 being freely passable through the apertures 152 and engageable with the corresponding prongs 8. The panel board 150 is further provided with a pair of apertures 156 positioned corresponding to the mounting screws 10 and countersunk to receive the external nuts 12, the screws 10 being passable therethrough and being secured in place by nuts 158 threadedly received thereby and engaging the underside of the panel 150. After the socket has been rigidly secured to the panel 150 by means of the screws 10 and nuts 158, the individual standard sockets 154 may he forced upwardly through the apertures 152 so as to receive therein the prongs 8.

One typical arrangement of electrical connections is shown in Fig. 10. The contact prongs 8 are shown grouped into three standard sets of fourteen each. Not all of the prongs are used. Thirty of the prongs, designated 8a, are individually connected to the individual movable contacts 44. Two of the prongs, designated 8b, are connected to the opposite ends of the bus bar 48 to which all of the fixed contacts 42 are connected. Two prongs 8b are used for purposes of electrical balance, but only one prong is absolutely necessary. Two other prongs designated 80 connect to the leads 166 of the electromagnet windings 84, 85' a register 160 having a negative temperature coefiicient of resistance being interposed in series therewith, as is conventional, in order to render the operations independent of ambient temperature.

Under normal conditions the armature 52 will pivot in a substantially frictionless manner about the edge 50 of the mounting plate 20, the leaf spring 76 exerting no appreciable restraining or restoring effect with respect to that pivotal motion. Since the leaf spring 76 is fixedly connected on the one hand to the forwardly projecting portion 52 of the mounting plate 20 and on the other hand to the first portion 54 of the armature 52, and since that spring 76 is non-extensible, it will prevent the armature 52 from moving along the plate 29 in a direction toward the rear of the unit, that is to say, away from the portion of the unit where the contact pairs 42, 44 are mounted. Because the leaf spring 76 is mounted in a straight condition it will strongly resiliently oppose any tendency toward buckling, and hence will resiliently resist any movement of the armature 52 toward the front of the unit. It thus normally positions the armature accurately with respect to the mounting plate 20, so that there is no interference between the apertures 62 in the armature wing portions 60 and the upper portion 64 of the front lower spacers 28. In this position of the armature 52, the disks 72 are spaced slightly forwardly from the plate edge 50 so as to permit the desired degree of pivotal movement of the armature 52. The interengagement between the disks 72 and the ledges 66 defined by the upper surfaces of the upper portion 64 of the front lower spacers 28 will prevent the armature 52 from moving downwardly away from the plate 20.

Any vibratory, accelerative or shock forces which might tend to move the armature 52 downwardly will have no effect thereon, the interengagement between the disks 72 and the ledges 66 positively preventing such movement. Any such forces tending to move the armature 52 in a rearward direction will be positively prevented by the non-extensible nature of the leaf spring 76. Any such forces tending to move the armature 52 forwardly will be resiliently resisted by the leaf spring 76, that spring buckling in opposition to such movement. The degree of such movement is positively limited either by engagement of the disks 72 with the plate edge 51 or by engagement of the armature 52 at its apertures 62 with the front spacer portions 64. The normal clearance between these cooperating elements is carefully set so that this limited degree of movement will be less than that which would give rise to any permanent deformation in the spring 76, and hence when such forces are relieved the spring 76 will restore the armature 52 to its normal position.

When the armature 52 is at rest, the reference springs 130, pulling upwardly on the plate 122, cause the armature arms 114 to move upwardly and pivot with respect to the plate 122, the flexibility of the plate 122 and the edgecontact between it and the armature arms 114 permitting this relative movement in a substantially frictionless manner and the orientation of the sheet 122 relative to the arms 114 being such that no permanent distortion occurs. The lifting of the armature arms 114 causes the armature to pivot about the mounting plate edge 50 in a clockwise direction as viewed in Fig 4 until the disk 72 engages the 10 edge 50 or the rear end of the armature 52 engages the ledge 18, or both. This movement is accompanied by a slight flexing of the leaf spring 76 which offers no appreciable opposition thereto, the spacer portions 64 passing freely and without contact through the armature apertures 62 and the forwardly projecting mounting plate portion 53 passing freely and without contact through the armature opening 58. This pivotal'movement causes the first armature portion 54 to move away from the projecting portion of the electromagnet cores 86. When the electromagnet 82 is energized the first armature portion 54 is attracted toward the electromagnet, the armature pivots in a counter-clockwise direction as viewed in Fig. 4 and against the action of the reference springs 130,

g the plate 122 and contact-lifting member 118 are moved downwardly, and the lower inclined edge 120 of the contact lifting member 118 makes sequential engagement with the movable contacts 44, lifting them one by one from their respective fixed contacts 42 so as to open the circuits therebet-ween. As each of the movable contacts 44 is lifted from its fixed contact 42, it is resiliently distorted, and therefore exerts an action on the contact-lifting member 118 opposing the downward movement thereof, this force increasing as the number of movable contacts 44 engaged by the lower surface 121? of the contact lifting member 118 increases. The restoring force exerted by the reference spring 11% will also increase as the armature 52 continues to pivot in this counterclockwise direction. However, the magnetic attraction exerted by the armature cores 86 on the armature 52 will also increase, and at an increasing rate, because of the manner in which the air gap between the electromagnet 82 and the armature 52 decreases, as previously set forth.

While the armature is thus pivoted, the plate 122, held by the reference springs in substantially uniform alignment with respect to the movable contacts 44, is also pivoted with respect to the armature arms 114, this talcing place in a substantially frictionless manner and without any permanent distortion.

By reason of the specific mounting structure the position of the armature relative to the electromagnet is not only closely predetermined so that each unit will functoin substantailly like the next even on an industrial production basis, subject only to adjustment of the dashpot by means of the screw 142 and adjustment of the strength of the reference springs 136 by bending of the arms 132, but the performance of each unit is rendered substantially shockproof and vibration-resistant because the armature 52 is always positively constrained to move in a predetermined manner and in a predetermined position relative to the mounting plate 20 and the electromagnet 82. I

This application is a continuation of my application Ser. No. 330,259 filed January 8, 1953 and entitled Electromagnetic Unit, and now abandoned.

While but a single embodiment of the present invention is here disclosed, it will be apparent that many variations may be made therein as to details without departing from the spirit of the invention as defined in the following claims.

I claim:

1. In an electromagnetic unit, an electromagnet, an

end plate therefor, an armature having a first portion I overlying said end plate and adapted to be attracted by said electromagnet and a second portion extending beyond an edge of said end plate, said armature resting on said edge and said edge defining the fulcrum about which said armature pivots, and a leaf spring mounted in a substantially flat condition and located to one side of said edge, the ends of said leaf spring being secured respectively to said armature and said end plate.

2. In an electromagnetic unit, an electromagnet, an end plate therefor, an armature having a first portion overlying said end plate and adaptedto be attracted by said electromagnet and a second portion extending beyond said end plate, said armature being pivotally mounted relative to said end plate, a mounting element, a support between and operatively connected to said mounting element and said end plate for maintaining said end plate spaced from said element, said armature being positioned between said end plate and said element, a portion of said support defining a ledge facing said end plate, and a member carried by said armature and engaging said ledge, thereby preventing said armature from moving away from said end plate.

3. The electromagnetic unit of claim 2, in which said second armature portion extends beyond an edge of said end plate and in which said member is carried by said second armature portion and is opposite and closely spaced with respect to said end plate edge, thereby limiting the degree of pivotal movement of said armature.

4. The electromagnetic unit of claim 3, in which said end plate has a portion extending beyond said end plate edge, said second armature portion has an aperture through which said end plate portion is adapted to freely pass when said armature pivots about said end plate edge, and a leaf spring mounted in a substantially fiat condition and secured to said extending end plate portion and to said first armature portion, thereby positively preventing movement of said armature along said end plate in a direction from said edge away from said electromagnet and resiliently resisting movement of the armature in the opposite direction.

5. The electromagnetic unit of claim 2, in which said second armature portion extends beyond an edge of said end plate and said end plate has a portion extending beyond said end plate edge, said second armature portion has an aperture through which said end plate portion is adapted to freely pass when said armature pivots about said end plate edge, and in which a leaf spring is mounted in a substantially flat condition and secured to said extending end plate portion and to said first armature portion, thereby positively preventing movement of said armature along said end plate in a direction from said edge away from said electromagnet and resiliently resisting movement of the armature in the opposite direction.

6. The electromagnetic unit of claim 1, in which said end plate has a portion extending beyond said end plate edge, said second armature portion has an aperture through which said end plate portion is adapted to freely pass when said armature pivots about said end plate edge, and in which said leaf spring is secured to said extending end plate portion and to said first armature portion, thereby positively preventing movement of said armature along said end plate in a direction from said edge away from said electromagnet and resiliently resisting movement of the armature in the opposite direction.

7. The electromagnetic unit of claim 2, in which a leaf spring has its ends secured respectively to said armature and said end plate, and said armature is provided with an aperture through which said support freely passes, the clearance between said armature aperture and said support being sufficiently great to permit said armature to pivot within its desired limits and said clearance being less than the smallest distance which one end of said leaf spring may move toward the other and produce permanent distortion of said spring.

8. The electromagnetic unit of claim 2, in which a leaf spring has its ends secured respectively to said armature and said end plate, and said armature and the remainder of said unit have elements normally spaced'from one another in the direction parallel to said end plate from one end of said leaf spring to the other, said elements being engageable when said armature moves over said end plate in a direction such as to cause said spring to shorten in length, the spacing between said elements being less than the smallest distance which one end of said leaf spring may move toward the other and produce permanent distortion of said spring.

9. In an electromagnetic unit, an electromagnet, an end plate therefor, an armature having a first portion overlying said end plate and adapted to be attracted by said electromagnet and a second portion extending beyond said end plate, said armature being pivotally mounted relative to said end plate, a mounting element, a support between said mounting element and said end plate for maintaining said end plate spaced from said mounting element, said armature being positioned between said end plate and said mounting element and having an aperture through which said support loosely passes, a portion of said support passing through said aperture and defining a ledge facing said end plate and substantially in line with the end plate surface on which said armature is mounted, and a member carried by said armature on the surface thereof adjacent said end plate, extending partially over said armature aperture, and engaging said ledge, thereby retaining said armature close to said end plate.

10. The electromagnetic unit of claim 9, in which said member is carried by said second armature portion, and is opposite and closely spaced with respect to said end plate edge, thereby limiting the degree of pivotal movement of said armature.

11. The electromagnetic unit of claim 10, in which said armature extends beyond an edge of said end plate and said end plate has a portion extending beyond said end plate edge, said second armature portion has an aperture through which said end plate portion is adapted to freely pass when said armature pivots about said end plate edge, and in which a leaf spring is mounted in a substantially flat condition with one end thereof secured to said extending end plate portion and the other end thereof secured to said first armature portion, thereby positively preventing movement of said armature along said end plate in a direction tending to elongate said spring and resiliently resisting movement of the armature in the opposite direction.

12. The electromagnetic unit of claim 9, in which said armature extends beyond an edge of said end plate and said end plate has a portion extending beyond said end plate edge, said second armature portion has an aperture through which said end plate portion is adapted to freely pass when said armature pivots about said end plate edge, and in which a leaf spring is mounted in a substantially flat condition with one end thereof secured to said extending end plate portion and the other end thereof secured to said first armature portion, thereby positively preventing movement of said armature along said end plate in a direction tending to elongate said spring and resiliently resisting movement of the armature in the opposite direction.

13. In the electromagnetic unit of claim 9, a leaf spring the ends of which are secured respectively to said armature and said end plate, the clearance between said armature aperture and the portion of the support passing therethrough being less than the smallest distance which one end of said leaf spring may move relative to the other and produce permanent distortion of said spring.

14. In the electromagnetic unit of claim 9, a leaf spring the ends of which are secured respectively to said armature and said end plate, said armature and the remainder of said unit having elements normally spaced from one another in the direction parallel to said end plate from one end of said leaf Spring to the other, said elements being engageable when said armature moves over said end plate in a direction such as to cause said spring to shorten in length, the spacing between said elements being less than the smallest distance which one end of said leaf spring may move toward the other and produce permanent distortion of said spring.

15. In an electromagnetic unit, an electromagnet, an end plate therefor, an armature having a first portion 13 overlying said end plate and adapted to be attracted by said electromagnet and a second portion extending beyond an edge of said end plate, said armature being pivotally mounted relative to said end plate, the outer surfaces of said second armature portion having notches formed therein, and a plate pivotally secured to said second armature portion and extending substantially at right angles thereto, said plate having a slot into which said second armature portion is received, said slot having inclined outer surfaces adapted to seat within the notches in said arms.

16. The electromagnetic unit of claim 15, in which downwardly extending notches are provided at the bottom of said slot adjacent said inclined outer surfaces.

17. An electromagnetic unit comprising an electromagnet, an armature pivotally mounted with respect thereto and comprising a first portion overlying said electromagnet and adapted to be attracted thereby and a second portion extending from said electromagnet and having notche in the outer surfaces thereof, and a thin flexible plate pivotally secured to said second armature portion and extending substantially at right angles thereto, said plate having a slot into which said second armature portion is received, said slot having inclined outer surfaces adapted to seat within the notches in said arms.

18. The electromagnetic unit of claim 17, in which downwardly extending notches are provided at the bottom of said slot adjacent said inclined outer surfaces.

19. An electromagnetic unit comprising an electromagnet, an armature pivotally mounted with respect thereto and comprising a first portion overlying said electromagnet and adapted to be attracted thereby and a second portion extending from said electromagnet and comprising a pair of spaced projecting arms having notches in the outer surfaces thereof, and a plate pivotally secured to said arms and extending substantially at right angles thereto, said plate having a pair of slots into which said arms are received, each of said slots comprising a horizontal portion adapted to receive one of 14 said arms and an access portion communicating therewith, extending to an edge of said plate, and having an inclined outer surface adapted to seat within the notch in said one of said arms.

20. The electromagnetic unit of claim 19, in which a downwardly extending notch is provided at the bottom of each of said slots where said horizontal portion meets the inclined outer surface of said access portion.

21. In an electromagnet, a coil, a core within and projecting beyond said coil, an end plate against which said coil is mounted and having an aperture through which said core projects, said end plate having a slot under said coil and extending out beyond the periphery of said coil through which a coil lead is adapted to pass to the end thereof and then escape from said end plate, and an armature mounted against the other surface of said end plate and having a portion extending over and adapted to be attracted by said core, said slot permitting threading of said coil lead without interfering with the movement of said armature. 22. In an electromagnet, a coil, a core within and projecting beyond said coil, an end plate against which said coil is mounted and having an aperture through which said core projects, said end plate having a slot under said coil and extending out beyond the periphery of said coil, said end plate having a second aperture adjacent the end of said slot, a coil lead being adapted to pass through said slot to the end thereof, then escape from said end plate, and then pass through said second aperture, and an armature mounted against the other surface of said end plate and having a portion extending over and adapted to be attracted by said core, said slot and said second aperture permitting threading of said coil lead without interfering with the movement of said armature.

References Cited in the file of this patent UNITED STATES PATENTS 2,755,356 Jucker July 17, 1956 

